1. Field of the Invention
The present invention relates to a method for producing hexaalkylborazine. Hexaalkylborazine is used to form, for example, an interlayer dielectric film for semiconductor, a barrier metal layer and an etching stopper layer.
2. Description of Related Art
With higher functionalization of information devices, design rule of LSI has been required to be finer year by year. In production of LSI with finer design rule, materials composing LSI should also have higher performance and fulfill function even on fine LSI.
For example, as for materials used for an interlayer dielectric film in LSI, high dielectric constant causes signal delay. In fine LSI, effects of the signal delay is particularly significant. Therefore, development of a new low dielectric material which can be used for an interlayer dielectric film has been needed. Also, it is necessary not only to have low dielectric constant but also superior characteristics such as humidity resistance, heat resistance, mechanical strength, etc. to be used as an interlayer dielectric film.
As a material to respond to these requirements, a compound having borazine ring backbone has been proposed (for example, see US Laid Open Patent No. 2002-58142). A compound having borazine ring backbone (borazine compound) has small molecular polarizability and thus a coated film formed provides low dielectric constant. Moreover, the coated film formed is superior in heat resistance.
As a borazine compound, various compounds have been proposed up to now (for example, see US Laid Open Patent No. 2003-100175). Hexaalkylborazine among borazine compounds, whose boron moiety and nitrogen moiety are both substituted with an alkyl group, has very superior characteristics as low dielectric material.
As a method for producing hexaalkylborazine, whose boron moiety and nitrogen moiety are substituted with an alkyl group, a method using a Grignard reaction is disclosed (for example, see D. T. HAWORTH and L. F. HOHNSTEDT, J. Am. Chem. Soc., 82, 3860 (1960), Howard Steinberg, Robert J. Brotherton, “ORGANOBORON CHEMISTRY”, John Wiley & Sons, p 244-).
Also disclosed is a method for synthesizing a borazine compound whose hydrogen atom bonded to boron is substituted with an alkyl group, wherein borazine is reacted with an alkene compound in the presence of RhH(CO)(PPh3)3 (see Paul J. Fazen and Larry G. Sneddon, Organometallics, 1994, 13, 2867-2877). In this method, however, a starting compound is borazine not substituted with an alkyl group, and thus a compound synthesized is a borazine compound substituted with an alkyl group only at boron moiety.